Classification of Vacuum Level

The so-called “vacuum” refers to a gaseous state where the pressure in a given space is less than 101325 Pascal (i.e. a standard atmospheric pressure around 101KPa).

The standard or unit of vacuum measurement is called vacuum level. In the international general standards and China’s current standard in force, the most commonly used unit in vacuum measurements is Pascal ( Pa.). 1 Pa is equal to 1N/㎡. The unit used in technical atmosphere is Bar.1Bar=1kgf/cm2. The unit now used less often is torr. 1Torr is defined as 1/760atm.

International general classification of vacuum levels

The international standard usually divides the vacuum into four levels: low vacuum, medium vacuum, high vacuum, and ultra-high vacuum. In absence of strict criteria, the vacuum levels are roughly divided as follows:

Low Vacuum Level   （< 105~102Pa）  —— The pressure difference obtained by low vacuum is used to clamp, lift and transport materials, as well as to vacuum and filtrate (e.g. vacuum cleaner, vacuum suction cups, etc.)

Medium Vacuum Level （< 102~10-1Pa） —— Medium vacuum is generally used to remove the gas or moisture that is retained and dissolved in the material, as well as for vacuum heat insulation and isolation (e.g. food vacuum freezing, vacuum drying, vacuum packaging, etc.)

High Vacuum Level  （< 10-1~10-5Pa） ——vacuum smelting, vacuum coating, and manufacturing of vacuum devices can be done by using the characteristics of low density of residual gas and weak chemical action of any substance in high vacuum. A typical product is vacuum insulated glass. Vacuum insulated glass refers to the glass consisting of two or more pieces of flat glass with micro supporting spacers inside and edges sealed to create vacuum chamber in between. In principle, the vacuum level inside the vacuum insulated glass is lower than 10-1pa, so that the factors such as heat transfer by gas and sound transmission can be ignored.

Ultra-high Vacuum Level  （< 10-5Pa） —— In the ultra-high vacuum state, there is almost no atoms or molecules. It can be used for simulation of a space environment, as well as researches on surface physics and surface chemistry, etc. 

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Thermal Resistance, Thermal Conduction, Thermal Conductance, Heat Transfer Resistance

Thermal Resistance is a heat property and a measurement of a temperature difference by which an object or material resists a heat flow.

The law of heat transfer can be compared to the “Ohm’s Law” that describes the law related to the electricity transfer in electrical science.  

Ohm’s Law: I=U/R

where I is the electrical current flowing through the circuit; △V is the voltage drop between the two ends of the circuit and the electromotive force that drives the flow of electricity; R is the resistance of the resistor, representing the resistance in electricity transfer. 

A similar formula in the process of plane heat transfer is: Φ=T/R where Φ is the amount of heat flow transferred; T is the temperature difference between the two ends and the force that drives the heat flow; R is the thermal resistance representing the resistance in heat transfer. 

An object with better thermal conductivity generally has lower thermal resistance, measured in ℃/W or K/W.

Thermal Conduction is the reciprocal of thermal resistance, i.e. C=1/R，in W·m-2·K-1. 

Thermal Conductance, also known as heat transfer coefficient, refers to the quantity of heat that passes in unit time through an object of 1㎡ area and 1 m thickness when its opposite surfaces differ in temperature by 1K under steady state conditions. The legal measuring unit in China is W·m-1·K-1.  

Heat Transfer Resistance is the inverse of heat transfer coefficient, measured in W-1·㎡·K. The greater the heat transfer resistance, the better the thermal insulation performance. 

Definition, Harms, and Grading Standard of Noise

By physical definition, noise is the sound that delivers completely irregular oscillations in amplitude and frequency. From the perspective of environmental protection, noise is the unwanted sound. 

The distinctive characteristic of noise is that: there is no visible pollutant; it does not generate energy accumulation; it lasts for limited time and is transmitted in limited distance; noise disappears along with the vibration source and cannot be controlled through centralized systems. Noise could come from transportation, machinery and equipment in factories, construction work as well as the social and family activities of ordinary people. 

Noise can harm human beings in many aspects, including hearing loss, sleep disturbances, physical and psychological disorders. Working in an environment with a noise level of 100 dB could make people feel unpleasant, uncomfortable, and even suffer from temporary hearing loss.Noise louder than 140 dB will cause eyeballs to vibrate, vision blurring， and fluctuation of respiration, pulse, and blood pressure. It may even cause blood vessels to contract throughout your body, reduction in blood supply, and adverse effect on speaking ability.

dB is the standard unit of measurement for noise, called decibel. It is the unit for expressing the ratio of power. 

dB Levels
0-20 dB	Very quiet, hard to hear
20-40 dB	Quiet, whisper
40-60 dB	Normal indoor conversation
60-70 dB	Loud, harmful to nerve
70-90 dB	Very loud, could cause damage to nerve cells
90-100 dB	Intensified noise, hearing impaired
100-120 dB	Unbearable, temporary hearing loss with only one minute of exposure.
Greater than 120 dB	Itching or pain in the ear, extremely or totally deaf
About 300 dB or higher	Permanent hearing loss

The national noise emission standard for social environment are as follows:

Type	Applicable areas	Limitation unit：Leq：[dB(A)]
		Daytime	Nighttime
0	For rehabilitation or other purposes that requires an extremely quiet environment	50	40
1	For residential, health care, cultural and educational, scientific research, and administrative office areas that require a quiet environment.	55	45
2	For commercial, trading, and a hybrid of residential, commercial, and industrial purposes that need to maintain the quiet residential environment.	60	50
3	For industrial, logistics, and storage purposes that need to prevent industrial noises from causing serious impact on the surrounding environment.	65	55
4	For areas within a certain distance on both sides of the main traffic lines that require to prevent traffic noises from causing severe impact on the surrounding environment.	70	55

Hertz is also a unit of frequency in the international system of units. It measures the repetitive times of cyclical variation per second. Its symbol is Hz.  Noise can be divided into low frequency noise, medium frequency noise and high frequency noise according to the sound frequency. 

Low frequency noise refers to sounds with frequencies below 500 Hz.  

There are five main types of low-frequency noise sources in China’s residential communities: elevators, transformers, water pumps in high-rise buildings, central air conditioning systems, and traffic.  

Medium frequency noise refers to sounds with frequencies between 500～1000 Hz. Normal conversation in daily life and the sounds of most musical instruments are in the range of medium frequency.  

High frequency noise refers to sounds with a frequency greater than 1000 Hz.  High-frequency noises come from modern means of transport that we are familiar with, such as cars, trains, motorcycles, tractors, and airplanes, as well as the noises generated by tweeters, construction sites, shopping malls, sports and recreational venues, etc.

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Vacuum-degassing

When a variety of materials that makes up the vacuum insulated glass, such as glass, stainless steel, getter, and glass solder, are exposed to air, the surface of the material will absorb and dissolve a certain amount of gas. It later becomes the source of gas released by the materials sealed between the layers of the vacuum insulated glass. Vacuum insulated glass is the type of small volume vacuum unit that has a large surface area. A piece of 1 m2 vacuum insulated glass has an inner cavity with a volume equivalent only to the size of a ping-pong ball. Therefore, the gas released in the chamber of the vacuum insulated glass will have a great impact on the level of vacuum. For vacuum insulated glass degassed and sealed under room temperature, its level of vacuum will degrade rapidly within hours. The degassing process of vacuum insulated glass requires not only to fully discharge the gas inside the chamber, but also to bake the entire piece of glass to a certain temperature to release the gas absorbed by the surfaces and dissolved in the materials to the cavity for degassing. 

As glass is the main material that makes up the vacuum insulated glass, the degassing temperature must first consider the degassing requirements of the glass material. The gas sources of glass during baking come primarily from its surface, surface layer, and inner layer.

1.  Glass surface

There is a large amount of OH- existing on the surface of the glass, which has a very strong affinity to water. As such, the glass surface attracts a large number of water molecules and a small amount of CO2. Some gas is bonded with the glass surface only through physical attraction or weak chemical attraction. Heating it in vacuum to approximately 150℃ will release the gas molecules in a couple of minutes.  

2.  Weathered surface

The sodium calcium glass used in vacuum insulated glass contains a considerable amount of alkaline oxide which has poor chemical stability and is susceptible to moisture corrosion and weathering. The weathered layer is generally a few microns thick. The gas contained is mainly H2O. When the glass is heated to a certain temperature in a vacuum environment, the water will be released smoothly from the Si-OH-OH-Si structure to form Si-O-Si+H2O. The weathered layer of the glass is then restored. The gas in the glass surface can be removed by baking in a vacuum state for about 1 hour. The weathered layer can also be removed by baking in dry air with a humidity level less than 60% for about 1 hour. The effect is comparable to that of vacuum degassing. 

3.  Inside of glass body

The body of the glass contains a large amount of gas, mainly H2O and a small amount of CO2, O2 and SO2. It takes certain amount of time to bake and degas.  

After the degassing process, as long as the working temperature of the glass does not exceed 300℃, the discharge of gas in the glass has minimal effect on the level of vacuum of the device and can therefore be neglected.  

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Chemical Stability of Glass

Chemical stability: the ability of a substance to maintain its original physical and chemical properties under the influence of chemical factors. 

The chemical stability of glass refers to the resistance of glass towards erosion by chemical solutions during the process of use such as water, acid, alkali, salt, gas, etc.  It depends on the resistance of the glass against corrosion and the type and characteristics of the erosion medium (water, acid, alkali, and atmospheric agents, etc.). 

Main factors affecting the chemical stability of glass: 

1. Chemical components

（1） The water resistance and acid resistance of silicate glass mainly depend on content of the silicon, oxygen and alkali metal oxide.

（2） When the glass contains two kinds of alkali metal oxides at the same time, some extreme values will emerge in the chemical stability of the glass due to the “mixed alkali effect”.

（3）The chemical stability of the glass will decrease when the silicon oxide in silicate glass is replaced with an alkaline earth metal or other metal dioxides. But the reducing effect is less than that of the alkali metal. 

2.  Heat treatment

（1） Generally speaking, annealed glass enjoys the higher chemical stability than tempered glass.

（2） When glass is processed with open flame in the annealing process, its chemical stability will be increased.  On the contrary, if glass is annealed in flameless fire, its chemical stability will decrease.    

（3） Phase separation will occur during the annealing process of borosilicate glass. Its chemical stability is related to the resulting structure after phase separation.  

3. Surface state

（1）  The corrosion of glass by medium occurs first on the surface, and the glass surface state has great effect on chemical corrosion resistance. 

（2） Therefore, the glass surface state can be improved with the help of various surface treatments.  

4. Temperature and pressure

（1）The chemical stability of glass varies greatly with an increase in temperature.  

（2）Pressure also has a great effect. 

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Argon

Argon (Ar) is a relatively common noble gas. GB number 22011. CAS number 7440-37-1. Its molecular weight is 39.95. Colorless and odorless; Vapor pressure: 202.64 kPa(-179℃); Melting point: -189.2℃; Boiling point: -185.7℃; Solubility: slightly soluble in water; Relative density (water =1): 1.40(-186℃); Relative density (air =1): 1.38; Chemical stability: stable; Hazard mark: 5 (non-combustible gas).

Argon and the insulating glass

The density and dynamic viscosity of argon are higher than that of air while its thermal conductivity and specific heat capacity are lower. Argon is present in air at 1%, making it the most economical inert gas when compared with krypton and xenon. If the space between the two panes of insulating glass is filled with Argon gas, it can lower the heat convection and conduction between the sheets of glass, therefore, mitigate the overall thermal conductivity and reduce the K value of the insulating glass.

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Thermostability

Thermostability refers to the material’s ability to withstand rapid changes in temperature without destruction, also known as thermal-shock resistance. The thermostability of the general inorganic materials is proportional to their tensile strength, and inversely proportional to the elastic modulus and thermal expansion coefficient. Also, the thermal conductivity, heat capacity, and density exert impact on the thermal stability to a certain degree. The thermostability of architecture refers to the ability of a building envelope or room to resist temperature fluctuations under periodic thermal conditions.

Generally inorganic materials have poor thermostability. There are two types of damages caused by thermal shock: one type is the material fracture. The property of the material to resist such damage is called the resistance to thermal shock fracture; the other type is that under the thermal shock cycling, the material surface cracks and peels off which will eventually lead to fragmentation or qualitative change. The property of the material to resist such damage is called the resistance to thermal shock damage. The resistance to thermal shock fracture is a property especially important to brittle materials or low ductile materials. For high ductile materials, thermal fatigue is the main problem. Although the temperature change is not as harsh as thermal shock, its thermal stress level may also be close to the yield strength of the material. Further, the repetitive occurrence of such temperature change will eventually lead to fatigue breakdown.

To improve the thermostability of brittle materials such as compact ceramics and glass, the key is to improve their resistance to thermal shock fracture. The measures are as follows:

1. Increase the strength of the material and reduce the modulus of elasticity: this means that the increase of material flexibility to absorb more elastic strain energy without cracking, thus improving its thermostability.  

2. Improve the thermal conductivity of the material: the higher the thermal conductivity, the faster the heat transfers. It can effectively alleviate and balance the temperature difference between the inside and outside of the material, and reduce the accumulation of short-term thermal stress, which is beneficial to the improvement of thermostability.  

3. Reduce the thermal expansion coefficient of the material: Materials with a smaller thermal expansion coefficient produces lower thermal stress under the same temperature difference, therefore, have higher thermostability.  

4. Reduce the surface heat transfer coefficient: The smaller the coefficient, the greater the temperature change that the material can withstand and the higher thermostability it has.  

5. Reduce the effective thickness of the product: Thin material has shorter heat transfer path and is easier to distribute temperature quickly and evenly. 

For porous, coarse-grained, dry-pressed products and some sintered products, the key to improve their thermostability is to increase the resistance to thermal shock damage. The measures are as follows:

1. Reduce the strength of the material and increase the elastic modulus, so that the material stores less elastic strain energy during expansion and shrinkage that can cause cracks.  

2. Select materials with larger fracture surface energy to absorb more energy to stop cracking quickly once it cracks.

Air tightness, Water tightness and Wind-load Resistance of Building Exterior Doors and Windows

Air tightness, Water tightness and Wind-load Resistance of Building Exterior Doors and Windows

The three physical properties of building fenestration system generally refer to the air tightness, water tightness, and wind-load resistance. These three properties are the required items in fenestration testing. In 1986, China enacted the inspection standard for the three physical properties of building exterior doors and windows.  The standard was later updated in 2002. The new national standard was revised in the following aspects:

1.  Add the rate of air permeability per unit area as a rating indicator, to derive comprehensive rating when combined with the rate of air permeability per unit seam length rating indicator.  

2.  Add the content of inspecting air permeability rate under negative pressure differential.

3.  Specify the scope of use of the pressure fluctuation on water tightness performance.  

4.  Add the content of engineering inspection over the performance of wind-load resistance.

Air permeability performance, also known as air tightness, refers to the resistance of the closed exterior doors and windows to air leakage. The airtight performance of the exterior doors and windows has a great impact on the heat loss.  The better the airtight performance, the lesser the thermal exchange and the impact on room temperature. The measurement of air tightness takes the air penetration per unit seam length and unit area under standard condition when the pressure difference between the inside and outside the window equals to 10 Pa as the rating indicator. The air tightness is divided into 8 levels. The higher the number, the lesser the heat loss and the better the air tightness. Good air permeability is conducive to energy conservation and environmental protection.

The performance rating of the air tightness of exterior doors and windows
Level	Rating indicator q1	Rating indicator q2
1	4.0≥q1＞3.5	12.0≥q2＞10.5
2	3.5≥q1＞3.0	10.5≥q2＞9.0
3	3.0≥q1＞2.5	9.0≥q2＞7.5
4	2.5≥q1＞2.0	9.0≥q2＞7.5
5	2.0≥q1＞1.5	6.0≥q2＞4.5
6	1.5≥q1＞1.0	4.5≥q2＞3.0
7	1.0≥q1＞0.5	3.0≥q2＞1.5
8	q1≤0.5	q2≤1.5

Unit of indicator value:

q1: Indicator value per unit open seam. Measuring unit is m3/(m·h);

q2: Indicator value per unit area. Measuring unit is m3/(m2·h)

The data are extracted from “Graduations and Test Methods of Air Permeability， Water tightness， and Wind Load Resistance Performance for Building External Windows and Doors”.

Water tightness refers to the resistance of the closed exterior doors and windows to water leakage under wind and rain at the same time. General testing of the water tightness of exterior doors and windows is conducted according to the standard set forth in the “Graduations and Test Methods of Air Permeability ,Water tightness and Wind Load Resistance Performance for Building External Windows and Doors”, which specifies in detail the testing equipment requirements, performance testing methods, and the rating  indicators for water tightness. The testing devices simulate the condition of exterior doors and windows in the stormy weather, measure the pressure difference between the two sides of the doors and windows using pressure supply system, water supply system, pressure and water flow measuring system to determine the pressure differential during severe leakage, and finally identify the water tightness factor and rating of the doors and windows. The water tightness of doors and windows is divided into 6 levels with a higher level representing stronger water tightness. The doors and windows with good waterproof performance can effectively prevent the intrusion of rainwater into their internal structure to ensure a longer service life.

The performance rating of the water tightness of exterior doors and windows
Level	Rating indicator（Unit: Pa）
1	100≤△P＜150
2	150≤△P＜250
3	250≤△P＜350
4	350≤△P＜500
5	500≤△P＜700
6	△P≥700

△P is the pressure difference in a severe leakage. As defined in the national fenestration standard, it represents the pressure difference when a severe leakage in the testing samples of the exterior doors and windows occurs.

Severe leakage refers to: continuous spout from the test sample interface; continuous flow out of the test sample interface.  

Level 6 should have the specific testing pressure indicated after rating. The data are extracted from “Graduations and Test Methods of Air Permeability Water tightness and Wind Load Resistance Performance for Building External Windows and Doors”. 

Wind-load resistance refers to the resistance of the closed doors and windows to wind pressure without any damages (e.g. cracking, panel breakage, local yield, bonding failure, etc.) and functional impairment such as loose hardware and opening difficulties. There are up to 9 levels of wind resistance for doors and windows. The higher the number, the stronger the wind-load resistance. It is worth noting that the wind-load resistance level is not the same as the typhoon level. Wind load resistance level 9 indicates that the window can withstand more than 5000 Pa of wind pressure, easily resisting the destructive force of the Category 12 hurricane.

The performance rating of the wind-load resistance of exterior doors and windows
Level	Rating indicator（Unit: kPa）
1	1.0≤P＜1.5
2	1.5≤P＜2.0
3	2.0≤P＜2.5
4	2.5≤P＜3.0
5	3.0≤P＜3.5
6	3.5≤P＜4.0
7	4.0≤P＜4.5
8	4.5≤P＜5.0
9	P≥5.0

The data are extracted from “Graduations and Test Methods of Air Permeability Water tightness and Wind Load Resistance Performance for Building External Windows and Doors”.

Level 9 should have the specific testing pressure indicated after rating.